Light emitting diode, method of fabricating the same and led module having the same

ABSTRACT

Disclosed are a light emitting diode (LED), an LED module including the same, and a method of fabricating the same. The light emitting diode includes a first conductive-type semiconductor layer; a second conductive-type semiconductor layer; an active layer interposed between the first conductive-type semiconductor layer and the second conductive-type semiconductor layer; a first electrode pad region electrically connected to the first conductive-type semiconductor layer; a second electrode pad region electrically connected to the second conductive-type semiconductor layer; and a spark gap formed between a first leading end electrically connected to the first electrode pad region and a second leading end electrically connected to the second electrode pad region. The spark gap can achieve electrostatic discharge protection of the light emitting diode.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of and, claims the benefits andpriorities to, U.S. patent application Ser. No. 14/848,232, filed onSep. 8, 2015, and Patent Cooperation Treaty (PCT) Application No.PCT/KR2014/006904, filed on Jul. 29, 2014, which further claimspriorities from and the benefits of Korean Patent Application No.10-2013-0089414, filed on Jul. 29, 2013, and Korean Patent ApplicationNo. 10-2013-0089415, filed on Jul. 29, 2013, which are all herebyincorporated by reference for all purposes as if fully set forth herein.

TECHNICAL FIELD

Exemplary embodiments of the disclosed technology relate to a lightemitting diode (LED), an LED module including the same, and a method offabricating the same. For example, some implementations of the disclosedtechnology relates to a light emitting diode having improvedreliability, an LED module including the same, and a method offabricating the same.

BACKGROUND

Since GaN-based light emitting diodes were first developed, GaN-basedLEDs have been used for various applications including natural color LEDdisplays, LED traffic signboards, white LEDs, and the like.

Generally, a GaN-based light emitting diode is formed by growingepitaxial layers on a substrate such as a sapphire substrate, andincludes an N-type semiconductor layer, a P-type semiconductor layer andan active layer interposed therebetween. In addition, an n-electrode padis formed on the N-type semiconductor layer and a p-electrode pad isformed on the P-type semiconductor layer. The light emitting diode isconnected to an external power source through the electrode pads anddriven thereby. In this case, current flows from the p-electrode pad tothe n-electrode pad through the semiconductor layers.

On the other hand, a flip-chip type light emitting diode is used toprevent light loss due to the p-electrode pad while improving heatdissipation efficiency, and various electrode structures are proposed topromote current spreading in a large area flip-chip type light emittingdiode. Examples are disclosed in U.S. Pat. No. 6,486,499. For example, areflective electrode is formed on the P-type semiconductor layer, andextension legs are formed on a region of the N-type semiconductor layer,which is exposed by etching the P-type semiconductor layer and theactive layer, to facilitate current spreading.

The reflective electrode formed on the P-type semiconductor layerreflects light generated from the active layer to improve lightextraction efficiency and helps current spreading in the P-typesemiconductor layer. On the other hand, the extension legs connected tothe N-type semiconductor layer help current spreading in the N-typesemiconductor layer to allow uniform generation of light in a wideactive region. Particularly, a light emitting diode having a large areaof about 1 mm² and used for high power output requires current spreadingnot only in the P-type semiconductor layer but also in the N-typesemiconductor layer.

SUMMARY

Exemplary embodiments of the disclosed technology provide a lightemitting diode chip having an electrostatic discharge protectionfunction.

In addition, exemplary embodiments of the disclosed technology provide alight emitting diode which can be directly mounted on a printed circuitboard or the like using a solder paste by preventing diffusion of metalelements from the solder paste.

Further, exemplary embodiments of the disclosed technology provide alight emitting diode having improved current spreading performance.

Furthermore, exemplary embodiments of the disclosed technology provide alight emitting diode having improved light extraction efficiency byimproving reflectivity.

Furthermore, exemplary embodiments of the disclosed technology provide alight emitting diode capable of simplifying a manufacturing process byreducing the use of photomasks, an LED module including the same, and amethod of fabricating the same.

Additional features of the disclosed technology will be set forth in thedescription which follows, and in part will become apparent from thedescription, or may be learned from practice of the disclosedtechnology.

In accordance with one aspect of the present invention, a light emittingdiode includes: a first conductive-type semiconductor layer; a secondconductive-type semiconductor layer; an active layer interposed betweenthe first conductive-type semiconductor layer and the secondconductive-type semiconductor layer; a first electrode pad regionelectrically connected to the first conductive-type semiconductor layer;a second electrode pad region electrically connected to the secondconductive-type semiconductor layer; and a spark gap formed between afirst leading end electrically connected to the first electrode padregion and a second leading end electrically connected to the secondelectrode pad region. The spark gap can achieve electrostatic dischargeprotection of the light emitting diode.

The light emitting diode may further include an upper insulation layercovering the second conductive-type semiconductor layer. In addition,the upper insulation layer may include an opening that exposes the sparkgap. As the spark gap is exposed to the outside, it is possible toprevent generation of static electricity by electrical sparks via air.

The light emitting diode may include a mesa placed on the firstconductive-type semiconductor layer. The mesa includes the active layerand the second conductive-type semiconductor layer. The first electrodepad region may be electrically connected to the first conductive-typesemiconductor layer at a side of the mesa.

The light emitting diode may further include a reflective electrodestructure placed on the mesa; and a current spreading layer covering themesa and the first conductive-type semiconductor layer, and having anopening that exposes the reflective electrode structure. The currentspreading layer is electrically connected to the first conductive-typesemiconductor layer while being insulated from the reflective electrodestructure and the mesa. Further, the upper insulation layer may coverthe current spreading layer and the first leading end may be a portionof the current spreading layer.

The light emitting diode may further include an anti-diffusionreinforcing layer placed on the reflective electrode structure in theopening of the current spreading layer. Further, the second leading endmay be a portion of the anti-diffusion reinforcing layer. Further, theanti-diffusion reinforcing layer may be formed of the same material asthat of the current spreading layer.

In addition, the upper insulation layer may include a first opening thatexposes the current spreading layer to define the first electrode padregion, and a second opening that exposes the anti-diffusion reinforcinglayer to define the second electrode pad region.

The light emitting diode may further include a lower insulation layerplaced between the mesa and the current spreading layer and insulatingthe current spreading layer from the mesa. The lower insulation layerhas an opening placed in an upper region of the mesa and exposing thereflective electrode structure.

The spark gap may be placed between the first electrode pad region andthe second electrode pad region. The spark gap generates electric sparkswhen static electricity of high voltage is applied between the firstelectrode pad region and the second electrode pad region. To this end, agap between the first leading end and the second leading end may benarrower than other portions. Further, the first leading end and thesecond leading end may have a semi-circular or angled shape and faceeach other.

In accordance with another aspect of the present invention, a method offabricating a light emitting diode includes: forming a firstconductive-type semiconductor layer, an active layer and a secondconductive-type semiconductor layer on a substrate; patterning thesecond conductive-type semiconductor layer and the active layer to forma mesa on the first conductive-type semiconductor layer; and forming afirst electrode pad region electrically connected to the firstconductive-type semiconductor layer and a second electrode pad regionelectrically connected to the second conductive-type semiconductorlayer. Furthermore, the light emitting diode has a spark gap definedbetween the first leading end electrically connected to the firstelectrode pad region and the second leading end electrically connectedto the second electrode pad region.

The method may further include: forming a reflective electrode structureon the second conductive-type semiconductor layer; and forming a currentspreading layer covering the mesa and the first conductive-typesemiconductor layer, and having an opening exposing the reflectiveelectrode structure. Here, the current spreading layer forms ohmiccontact with the first conductive-type semiconductor layer while beinginsulated from the mesa.

The current spreading layer allows uniform spreading of current in thefirst conductive-type semiconductor layer. The first leading end may bea portion of the current spreading layer.

The method may further include forming an anti-diffusion reinforcinglayer on the reflective electrode structure. The anti-diffusionreinforcing layer may be formed together with the current spreadinglayer and the second leading end may be a portion of the anti-diffusionreinforcing layer. Thus, the first and second leading ends can be formedtogether with the current spreading layer and the anti-diffusionreinforcing layer by the same process.

The method may further include forming an upper insulation layercovering the current spreading layer. The upper insulation layer mayhave a first opening exposing the current spreading layer to define thefirst electrode pad region, and a second opening exposing theanti-diffusion reinforcing layer to define the second electrode padregion.

In addition, the upper insulation layer may further include an openingthrough which the first leading end and the second leading end areexposed. The opening may be distant from the first and second openings.

The method may further include forming a lower insulation layer coveringthe mesa and the first conductive-type semiconductor layer, beforeforming the current spreading layer. The lower insulation layer hasopenings that expose the reflective electrode structure and the firstconductive-type semiconductor layer.

The lower insulation layer may include a silicon oxide layer and theupper insulation layer may include a silicon nitride layer.

The method may further include forming an anti-Sn diffusion platinglayer on the first electrode pad region and the second electrode padregion using a plating technique.

In accordance with a further aspect of the present invention, a lightemitting diode includes: a first conductive-type semiconductor layer; amesa placed on the first conductive-type semiconductor layer andincluding an active layer and a second conductive-type semiconductorlayer; a reflective electrode structure placed on the mesa; a currentspreading layer covering the mesa and the first conductive-typesemiconductor layer, and having an opening that exposes the reflectiveelectrode structure, the current spreading layer being electricallyconnected to the first conductive-type semiconductor layer while beinginsulated from the reflective electrode structure and the mesa; and anupper insulation layer covering the current spreading layer. Inaddition, the upper insulation layer has a first opening exposing thecurrent spreading layer to define the first electrode pad region, and asecond opening exposing an exposed upper region of the reflectiveelectrode structure to define the second electrode pad region.

Since the first and second electrode pad regions are respectivelydefined by the first and second openings of the upper insulation layer,there is no need for a separate photomask for forming the first andsecond electrode pads.

On the other hand, an LED module includes a printed circuit board; andthe light emitting diode bonded to an upper side of the printed circuitboard. Here, the first electrode pad region and the second electrode padregion are bonded to corresponding pads on the printed circuit boardsvia solder pastes, respectively.

In some embodiments, the light emitting diode may further include ananti-Sn diffusion plating layer formed on the first electrode pad regionand the second electrode pad region.

Unlike typical AuSn solders in the related art, the solder paste is amixture of a metal alloy and an organic material and is cured by heattreatment to provide a bonding function. Thus, metal elements such as Snin the solder paste are unlikely to diffuse, unlike metal elements inthe typical AuSn solders in the related art.

The anti-Sn diffusion plating layer can prevent the metal elements suchas Sn in the solder paste from diffusing into the light emitting diode.Furthermore, as the anti-Sn diffusion plating layer is formed by aplating technique such as electroless plating, there is no need for aseparate photomask for formation of the plating layer.

In some embodiments, the light emitting diode may further include ananti-diffusion reinforcing layer placed on the reflective electrodestructure in the opening of the current spreading layer. Theanti-diffusion reinforcing layer may be exposed through the secondopening of the upper insulation layer. The anti-diffusion reinforcinglayer can prevent metal elements such as Sn in the solder paste fromdiffusing to the reflective electrode structure in the light emittingdiode.

The anti-diffusion reinforcing layer may be formed of the same materialas that of the current spreading layer.

Thus, the anti-diffusion reinforcing layer may be formed together withthe current spreading layer, and there is no need for a separatephotomask for formation of the anti-diffusion reinforcing layer.

The current spreading layer may include an ohmic contact layer, areflective metal layer, an anti-diffusion layer, and an anti-oxidationlayer. The current spreading layer may form ohmic contact with the firstconductive-type semiconductor layer through the ohmic contact layer. Forexample, the ohmic contact layer may be formed of Ti, Cr, Ni, and thelike.

The reflective metal layer reflects light incident on the currentspreading layer to increase reflectivity of the light emitting diode.The reflective metal layer may be formed of Al. In addition, theanti-diffusion layer prevents diffusion of metal elements and serves toprotect the reflective metal layer. Particularly, the anti-diffusionlayer can prevent diffusion of metal elements such as Sn in the solderpaste. The anti-diffusion layer may include Cr, Ti, Ni, Mo, TiW, W orcombinations thereof. Each of Mo, TiW and W may be used to form a singlelayer. On the other hand, Cr, Ti, and Ni may be used to form a pair oflayers.

Particularly, the anti-diffusion layer may include at least two pairs ofTi/Ni or Ti/Cr layers. The anti-oxidation layer is formed to preventoxidation of the anti-diffusion layer and may include Au.

The current spreading layer may have a reflectivity of 65% to 75%. Thus,the light emitting diode according to this embodiment of the inventioncan provide optical reflection by the current spreading layer inaddition to optical reflection by the reflective electrode structure,whereby light traveling through a sidewall of the mesa and the firstconductive-type semiconductor layer can be reflected.

The current spreading layer may further include a bonding layer placedon the anti-oxidation layer. The bonding layer may include Ti, Cr, Ni orTa. The bonding layer is used to enhance bonding strength between thecurrent spreading layer and the upper insulation layer.

The solder paste may adjoin the current spreading layer and theanti-diffusion reinforcing layer. Alternatively, the solder paste mayadjoin the anti-Sn diffusion plating layer formed on the currentspreading layer and the anti-diffusion reinforcing layer.

The reflective electrode structure may include a reflective metalsection; a capping metal section; and an anti-oxidation metal section.Furthermore, the reflective metal section may have a slanted sidesurface such that an upper surface of the reflective metal section has anarrower area than a lower surface thereof, and the capping metalsection may cover the upper and lower surfaces of the reflective metalsection. Further, the anti-oxidation metal section covers the cappingmetal section.

A stress relief layer may be formed at an interface between thereflective metal section and the capping metal section. The stressrelief layer relieves stress due to a difference in coefficient ofthermal expansion between the metal layers formed of differentmaterials.

In addition, the mesa may include elongated branches extending parallelto each other in one direction, and a connecting portion at which thebranches are connected to each other. The opening of the currentspreading layer may be placed on the connecting portion.

The light emitting diode may further include a lower insulation layerplaced between the mesa and the current spreading layer and insulatingthe current spreading layer from the mesa. The lower insulation layerhas an opening that is placed in an upper region of the mesa and exposesthe reflective electrode structure.

Furthermore, the opening of the current spreading layer may have agreater width than the opening of the lower insulation layer such thatthe opening of the lower insulation layer is completely exposedtherethrough. As a result, the current spreading layer can be insulatedfrom the reflective electrode structure.

On the other hand, the light emitting diode may further include ananti-diffusion reinforcing layer placed within the opening of thecurrent spreading layer and the opening of the lower insulation layer,and the anti-diffusion reinforcing layer may be exposed through thesecond opening of the upper insulation layer.

In addition, the lower insulation layer may include a silicon oxidelayer and the upper insulation layer may include a silicon nitridelayer. As the upper insulation layer is formed of silicon nitride, it ispossible to prevent diffusion of metal elements from the solder pastethrough the upper insulation layer.

In some embodiments, the solder paste may include lead-free solderalloys, for example, Sn—Ag alloys, Sn—Bi alloys, Sn—Zn alloys, orSn—Ag—Cu alloys.

The light emitting diode may further include a substrate and awavelength conversion layer covering a lower surface of the substrate.The substrate may be a growth substrate for growing the semiconductorlayers. In addition, the wavelength conversion layer may cover the lowersurface and a side surface of the substrate.

In accordance with yet another aspect of the present invention, a methodof fabricating a light emitting diode includes: forming a firstconductive-type semiconductor layer, an active layer and a secondconductive-type semiconductor layer on a substrate; patterning thesecond conductive-type semiconductor layer and the active layer to forma mesa on the first conductive-type semiconductor layer while forming areflective electrode structure on the mesa to form ohmic contact withthe mesa; forming a current spreading layer covering the mesa and thefirst conductive-type semiconductor layer, and having an opening thatexposes the reflective electrode structure, the current spreading layerforming ohmic contact with the first conductive-type semiconductor layerwhile being insulated from the mesa; and forming an upper insulationlayer covering the current spreading layer. On the other hand, the upperinsulation layer may have a first opening exposing the current spreadinglayer to define a first electrode pad region, and a second openingexposing an exposed upper region of the reflective electrode structureto define the second electrode pad region.

In the fabrication method, since there is no need for formation ofelectrode pads on the upper insulation layer, it is possible to reducethe number of photomasks for fabrication of the light emitting diode.

The method may further include forming an anti-diffusion reinforcinglayer on the reflective electrode structure. The anti-diffusionreinforcing layer can be formed together with the current spreadinglayer, and the second opening of the upper insulation layer can exposethe anti-diffusion reinforcing layer. Accordingly, the reflectiveelectrode structure can be concealed and protected by the anti-diffusionreinforcing layer and the upper insulation layer.

The method may further include forming a lower insulation layer coveringthe mesa and the first conductive-type semiconductor layer, beforeforming the current spreading layer; dividing the lower insulation layerand the first conductive-type semiconductor layer into chip regions bylaser scribing; and patterning the lower insulation layer to formopenings exposing the first conductive-type semiconductor layer and anopening exposing the reflective electrode structure.

Since a chip isolation region is formed using laser scribing, there isno need for use of a photomask. In addition, since laser scribing isperformed after formation of the lower insulation layer, particlesformed in the laser scribing process can be easily removed by cleaningthe lower insulation layer, whereby the light emitting diode can beprevented from being contaminated by the particles.

The lower insulation layer may include a silicon oxide layer and theupper insulation layer may include a silicon nitride layer.

The method may further include forming an anti-Sn diffusion platinglayer on the first electrode pad region and the second electrode padregion using a plating technique. The plating layer may be formed byelectroless plating such as ENIG (electroless nickel immersion gold) andthe like.

On the other hand, the substrate may be partially removed to have asmall thickness by grinding and/or lapping. Then, the substrate isseparated from the chip isolation region formed by laser scribing,thereby providing final individual chips separated from each other.Next, a wavelength conversion layer may be coated onto the lightemitting diode chips, and the light emitting diode having the wavelengthconversion layer is mounted on a printed circuit board via a solderpaste, thereby providing an LED module.

The wavelength conversion layer may be formed by coating aphosphor-containing resin, followed by curing the resin. Alternatively,the wavelength conversion layer may be formed by spraying phosphorpowder onto the light emitting diode chip using an aerosol apparatus.

According to embodiments of the disclosed technology, it is possible toprotect light emitting diodes from static electricity by forming a sparkgap. In addition, some implementations of the disclosed technologyprovide a light emitting diode, which can prevent diffusion of metalelements from a solder paste, and a method for fabricating the same.Further, some implementations of the disclosed technology provide alight emitting diode having improved current spreading performance, forexample, a flip-chip type light emitting diode having improved currentspreading performance. Furthermore, the light emitting diodes accordingto some implementations of the disclosed technology have improvedreflectivity by forming a current spreading layer, thereby providingimproved light extraction efficiency. Furthermore, the light emittingdiodes according to some implementations of the disclosed technology canomit a photolithography process for formation of electrode pads, and canreduce the number of photomasks by forming a chip isolation region usinga laser scribing technique.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of an exemplary LED module inaccordance with an embodiment of the disclosed technology.

FIG. 2( a) to FIG. 10 are views illustrating an exemplary method offabricating a light emitting diode in accordance with an embodiment ofthe disclosed technology, and in each of FIG. 2 to FIG. 9, (a) is a planview, (b) is a cross-sectional view taken along line A-A, and (c) is across-sectional view taken along line B-B.

FIG. 11( a) to FIG. 14( c) are views illustrating an exemplary method offabricating a light emitting diode in accordance with an embodiment ofthe disclosed technology, and in each of FIG. 11 to FIG. 14, (a) is aplan view, (b) is a cross-sectional view taken along line A-A, and (c)is a cross-sectional view taken along line B-B.

DETAILED DESCRIPTION

In the related art, the light emitting diode employs linear extensionlegs which have high resistance, which results in imposing some limit oncurrent spreading. Moreover, since the reflective electrode is placedonly on the P-type semiconductor layer, a substantial amount of light isabsorbed by the electrode pads and extension legs while not beingreflected by the reflective electrode and thus, substantial light lossis caused. When used in a final product, the light emitting diode isprovided by an LED module. The LED module generally includes a printedcircuit board and an LED package mounted on the printed circuit board,in which the light emitting diode is mounted in chip form within the LEDpackage. A typical LED chip is packaged after being mounted on asub-mount, a lead frame or a lead electrode by silver pastes or AuSnsolders. Then, the LED package is mounted on the printed circuit boardby solder pastes. As a result, pads on the LED chip are distant from thesolder pastes, and bonded to the printed circuit board by a relativelystable bonding material such as silver pastes, AuSn, and the like.

Recently, various attempts have been made to fabricate an LED module bydirectly bonding electrode pads of a light emitting diode to a printedcircuit board using solder pastes. For example, an LED module can befabricated by directly mounting an LED chip on a printed circuit boardinstead of packaging the LED chip. Otherwise, an LED module can befabricated by mounting a so-called wafer level LED package on a printedcircuit board. In these LED modules, since the electrode pads directlyadjoin the solder pastes, metal elements such as tin (Sn) diffuse fromthe solder pastes into the light emitting diode through the pads andcause short circuit in the light emitting diode and device failure.

GaN-based compound semiconductors are formed by epitaxial growth on asapphire substrate, the crystal structure and lattice parameter of whichare similar to those of the semiconductors, in order to reduce crystaldefects. However, the epitaxial layers grown on the sapphire substratecontain many crystal defects such as V-pits, threading dislocations, andthe like. When high voltage static electricity is applied to theepitaxial layers, current is concentrated at crystal defects in theepitaxial layers, causing diode breakdown. Thus, with respect toelectrostatic discharge or electrical fast transient (EFT), which is aspark generated in a switch, and lightning surge in air, securingreliability of LEDs becomes important.

Generally, in packaging of a light emitting diode, a Zener diode ismounted together with the light emitting diode to prevent electrostaticdischarge. However, the Zener diode is expensive and a process ofmounting the Zener diode increases the number of processes for packagingthe light emitting diode and manufacturing costs. Moreover, since theZener diode is placed near the light emitting diode in the LED package,the LED package has deteriorated luminous efficacy due to absorption oflight by the Zener diode and deteriorated LED package yield.

Hereinafter, exemplary embodiments of the disclosed technology will bedescribed in detail with reference to the accompanying drawings. Itshould be understood that the following embodiments are provided as someexamples of the disclosed technology to facilitate understanding of thedisclosed technology. Thus, it should be understood that the disclosedtechnology is not limited to the following embodiments and may beembodied in different ways. In addition, in the drawings, the width,length and thickness of components may be exaggerated for convenience.Further, it should be noted that the drawings are not to precise scale.Like components will be denoted by like reference numerals throughoutthe specification.

FIG. 1 is a schematic sectional view of an LED module in accordance withone embodiment of the disclosed technology.

Referring to FIG. 1, an LED module according to an exemplary embodimentof the disclosed technology includes a printed circuit board 51 havingpads 53 a and 53 b and a light emitting diode 100 bonded to the printedcircuit board 51 via solder pastes 55.

The printed circuit board has a printed circuit thereon, and anysubstrate capable of providing an LED module can be used as the printedcircuit board without limitation.

Conventionally, a light emitting diode is mounted on a substrate havinga lead frame or lead electrodes formed thereon, and a light emittingdiode package including such a light emitting diode is mounted on aprinted circuit board. According to some implementations, the lightemitting diode 100 is directly mounted on the printed circuit board 51via the solder pastes 55.

The light emitting diode 100 may include a flip-chip type light emittingdiode and be mounted upside down on the printed circuit board. To thisend, the light emitting diode 100 has a first electrode pad region 43 aand a second electrode pad region 43 b. The first and second electrodepad regions 43 a and 43 b may be formed in a recess shape on one surfaceof the light emitting diode 100.

On the other hand, a lower surface of the light emitting diode 100, forexample, a surface of the light emitting diode opposite the first andsecond electrode pad regions 43 a and 43 b, may be covered with awavelength conversion layer 45. The wavelength conversion layer 45 maycover not only the lower surface of the light emitting diode 100 butalso side surfaces of the light emitting diode 100.

In FIG. 1, the light emitting diode is schematically shown forconvenience of description. The structure and respective components ofthe light emitting diode will be more clearly understood in thefollowing description of a method of fabricating the light emittingdiode. Furthermore, it should be noted that light emitting diodesaccording to embodiments of the disclosed technology are not limited tothe structure in which the light emitting diode is directly mounted onthe printed circuit board.

FIG. 2( a) to FIG. 10 are views illustrating a method of fabricating alight emitting diode in accordance with an exemplary embodiment of thedisclosed technology. In each feature, (a) is a plan view, (b) is across-sectional view taken along line A-A, and (c) is a cross-sectionalview taken along line B-B.

First, referring to FIGS. 2( a) to 2(c), a first conductive-typesemiconductor layer 23, an active layer 25 and a second conductive-typesemiconductor layer 27 are grown on a substrate 21. The substrate 100enables the growth of a GaN-based semiconductor layer, and may include,for example, a sapphire substrate, a silicon carbide substrate, a GaNsubstrate, or a spinel substrate, and the like. In some implementations,the substrate may be or include a patterned substrate such as apatterned sapphire substrate.

For example, the first conductive-type semiconductor layer may includean n-type gallium nitride-based layer and the second conductive-typesemiconductor layer 27 may include a p-type gallium nitride-based layer.In addition, the active layer 25 may have a single quantum wellstructure or a multi-quantum well structure, and may include well layersand barrier layers. In addition, the composition of the well layers maybe determined according to the wavelength of light and may include, forexample, AlGaN, GaN or InGaN.

On the other hand, a pre-oxidation layer 29 may be formed on the secondconductive-type semiconductor layer 27. The pre-oxidation layer 29 maybe formed of or include, for example, SiO₂ by chemical vapor deposition.

Then, a photoresist pattern 30 is formed. The photoresist pattern 30 ispatterned to have openings 30 a. As shown in FIG. 2( a) and FIG. 2( b),the openings 30 a are formed such that an inlet of each opening has anarrower width than a bottom of the opening. The photoresist pattern 30having the openings 30 a of this structure can be easily formed using anegative type photoresist.

Referring to FIGS. 3( a) to 3(c), the pre-oxidation layer 29 is etchedusing the photoresist pattern 30 as an etching mask. The pre-oxidationlayer 29 may be etched by wet etching. As a result, the pre-oxidationlayer 29 in the openings 30 a of the photoresist pattern 30 is etched toform openings 29 a of the pre-oxidation layer 29, which expose thesecond conductive-type semiconductor layer 27. The bottom portions ofthe openings 29 a are generally similar or greater than the bottomportions of the openings 30 a of the photoresist pattern 30.

Referring to FIG. 4, a reflective electrode structure 35 is formed by alift-off technology. The reflective electrode structure 35 may include areflective metal section 31, a capping metal section 32 and ananti-oxidation metal section 33. The reflective metal section 31includes a reflective layer, and a stress relief layer may be furtherformed between the reflective metal section 31 and the capping metalsection 32. The stress relief layer relieves stress due to difference incoefficient of thermal expansion between the reflective metal section 31and the capping metal section 32.

The reflective metal section 31 may be formed of or include, forexample, Ni/Ag/Ni/Au, and may have an overall thickness of about 1600 Å.As shown, the reflective metal section 31 is formed to have a slantedside surface, for example, such that the bottom of the reflective metalsection has a relatively wide area. Such a reflective metal section 31may be formed by e-beam evaporation.

The capping metal section 32 covers upper and side surfaces of thereflective metal section 31 to protect the reflective metal section 31.The capping metal section 32 may be formed by sputtering or by e-beamevaporation, for example, planetary e-beam evaporation, in which vacuumdeposition is performed while rotating the substrate 21 in a slantedstate. The capping metal section 32 may include Ni, Pt, Ti, or Cr, andmay be formed by depositing, for example, about five pairs of Ni/Ptlayers or about five pairs of Ni/Ti layers. Alternatively, the cappingmetal section 32 may include TiW, W, or Mo.

A material for the stress relief layer may be selected in various waysdepending upon metal components of the reflective layer and the cappingmetal section 32. For example, when the reflective layer is composed ofor includes Al or Al-alloys and the capping metal section 32 is composedof or includes W, TiW or Mo, the stress relief layer may be or include asingle layer of Ag, Cu, Ni, Pt, Ti, Rh, Pd or Cr, or a composite layerof Cu, Ni, Pt, Ti, Rh, Pd or Au. In addition, when the reflective layeris composed of or includes Al or Al-alloys and the capping metal section32 is composed of or includes Cr, Pt, Rh, Pd or Ni, the stress relieflayer may be or include a single layer of Ag or Cu, or a composite layerof Ni, Au, Cu or Ag.

In addition, when the reflective layer is composed of or includes Ag orAg-alloys and the capping metal section 32 is composed of or includes W,TiW or Mo, the stress relief layer may be or include a single layer ofCu, Ni, Pt, Ti, Rh, Pd or Cr, or a composite layer of Cu, Ni, Pt, Ti,Rh, Pd, Cr or Au. Further, when the reflective layer is composed of orincludes Ag or Ag-alloys and the capping metal section 32 is composed ofor includes Cr or Ni, the stress relief layer may be or include a singlelayer of Cu, Cr, Rh, Pd, TiW or Ti, or a composite layer of Ni, Au orCu.

Further, the anti-oxidation metal section 33 includes Au in order toprevent oxidation of the capping metal section 32, and may be formed ofor include, for example, Au/Ni or Au/Ti. Since Ti secures adhesion of anoxide layer such as SiO₂, in some implementations, Ti can be used. Theanti-oxidation metal section 33 may also be formed by sputtering or bye-beam evaporation, for example, planetary e-beam evaporation, in whichvacuum deposition is performed while rotating the substrate 21 in aslanted state.

The photoresist pattern 30 is removed after deposition of the reflectiveelectrode structure 35, whereby the reflective electrode structure 35remains on the second conductive-type semiconductor layer 27, as shownin FIG. 4.

The reflective electrode structure 35 may include branches 35 b and aconnecting portion 35 a, as shown in FIG. 4. The branches 35 b may havean elongated shape and be parallel to each other. The connecting portion35 a connects the branches 35 b to each other. However, it should beunderstood that the reflective electrode structure 35 is not limited toa particular shape and may be modified into various shapes.

Referring to FIG. 5, a mesa M is formed on the first conductive-typesemiconductor layer 21. The mesa M includes the active layer 25 and thesecond conductive-type semiconductor layer 27. The active layer 25 isplaced between the first conductive-type semiconductor layer 23 and thesecond conductive-type semiconductor layer 27. The reflective electrodestructure 35 is placed on the mesa M.

The mesa M is formed by patterning the second conductive-typesemiconductor layer 27 and the active layer 25 so as to expose the firstconductive-type semiconductor layer 23. The mesa M may be formed to havea slanted side surface by photoresist reflow technology or the like. Theslanted profile of the side surface of the mesa M enhances extractionefficiency of light generated in the active layer 25.

As shown, the mesa M may include elongated branches Mb extendingparallel to each other in one direction and a connection portion Maconnecting the branches to each other. With such configuration of themesa, the light emitting diode can permit uniform spreading of electriccurrent in the first conductive-type semiconductor layer 23. Here, itshould be understood that the mesa M is not limited to a particularshape and may be modified into various shapes. On the other hand, thereflective electrode structure 35 covers most of the upper surface ofthe mesa M and generally has the same shape as the shape of the mesa Min plan view.

While the second conductive-type semiconductor layer 27 and the activelayer 25 are subjected to etching, the pre-oxidation layer 29 remainingon these layers is also partially removed by etching. On the other hand,although the pre-oxidation layer 29 can remain near an edge of thereflective electrode structure 35 on each of the mesa M, the remainingpre-oxidation layer 29 can also be removed by wet etching and the like.Alternatively, the pre-oxidation layer 29 may be removed beforeformation of the mesa M.

Referring to FIG. 6, after the mesa M is formed, a lower insulationlayer 37 is formed to cover the mesa M and the first conductive-typesemiconductor layer. The lower insulation layer 37 may be formed of orinclude an oxide layer such as SiO₂ and the like, a nitride layer suchas SiNx and the like, or an insulation layer of MgF₂ by chemical vapordeposition (CVD) and the like. The lower insulation layer 37 may be asingle layer or multiple layers. In addition, the lower insulation layer37 may be or include a distributed Bragg reflector (DBR) in which lowrefractive index material layers and high refractive index materiallayers are alternately stacked one above another. For example, aninsulating reflective layer having high reflectivity may be formed bystacking dielectric layers such as SiO₂/TiO₂, or SiO₂/Nb₂O₅, and thelike.

Then, a chip isolation region 23 h is formed by laser scribing to dividethe lower insulation layer 37 and the first conductive-typesemiconductor layer 23 into chip units. Grooves may be formed on theupper surface of the substrate 21 by laser scribing. As a result, thesubstrate 21 is exposed near an edge of the first conductive-typesemiconductor layer 23.

Since the first conductive-type semiconductor layer 23 is divided intochip units by laser scribing, it is possible to omit a separatephotomask for an isolation process. However, it should be understoodthat the disclosed technology is not limited to the isolation processusing laser scribing. For example, the first conductive-typesemiconductor layer 23 may be divided into chip units before or afterformation of the lower insulation layer 37 using a typicalphotolithography and etching technique.

As shown in FIG. 6, the mesa M may be formed to be placed only inside anupper region of the first conductive-type semiconductor layer 23. Forexample, the mesa M may be placed in an island shape on the upper regionof the first conductive-type semiconductor layer 23.

Next, referring to FIG. 7, the lower insulation layer 37 is subjected topatterning to form openings 37 a and 37 b in predetermined regions toallow electrical connection to the first conductive-type semiconductorlayer 23 and the second conductive-type semiconductor layer 27. Forexample, the lower insulation layer 37 may have openings 37 b whichexpose the first conductive-type semiconductor layer 23, and openings 37a which expose the reflective electrode structure 35.

The openings 37 a are placed only in upper regions of the mesas M, forexample, on the connecting portions of the mesas M. The openings 37 bmay be placed in regions between the branches Mb of the mesas M and nearthe edge of the substrate 21, and may have an elongated shape extendingalong the branches Mb of the mesas M.

Referring to FIG. 8, a current spreading layer 39 is formed on the lowerinsulation layer 37. The current spreading layer 39 covers the mesa Mand the first conductive-type semiconductor layer 23. In addition, thecurrent spreading layer 39 has an opening 39 a placed in the upperregion of the mesa M and exposing the reflective electrode structure 35.The current spreading layer 39 may form ohmic contact with the firstconductive-type semiconductor layer 23 through the opening 37 b of thelower insulation layer 37. The current spreading layer 39 is insulatedfrom the mesa M and the reflective electrodes 35 by the lower insulationlayer 37.

The opening 39 a of the current spreading layer 39 has a greater areathan the opening 37 a of the lower insulation layer 37 to prevent thecurrent spreading layer 39 from being connected to the reflectiveelectrode structures 35. Thus, the opening 39 a has sidewalls placed onthe lower insulation layer 37.

The current spreading layer 39 is formed on an overall upper region ofthe substrate 21 excluding the openings 39 a. Thus, electric current canbe easily dispersed through the current spreading layer 39.

The current spreading layer 39 may include an ohmic contact layer, areflective metal layer, an anti-diffusion layer, and an anti-oxidationlayer. The current spreading layer can form ohmic contact with the firstconductive-type semiconductor layer through the ohmic contact layer. Forexample, the ohmic contact layer may be formed of or include Ti, Cr, orNi, and the like. The reflective metal layer increases reflectivity ofthe light emitting diode by reflecting incident light entering thecurrent spreading layer. The reflective metal layer may be formed of orinclude Al. In addition, the anti-diffusion layer protects thereflective metal layer by preventing diffusion of metal elements. Forexample, the anti-diffusion layer can prevent diffusion of metalelements such as Sn within a solder paste. The anti-diffusion layer maybe composed of or include Cr, Ti, Ni, Mo, TiW, or W or combinationsthereof. The anti-diffusion layer may be a single layer including Mo,TiW or W. Alternatively, the anti-diffusion layer may include a pair ofCr, Ti or Ni layers. For example, the anti-diffusion layer may includeat least two pairs of Ti/Ni or Ti/Cr layers. The anti-oxidation layer isformed to prevent oxidation of the anti-diffusion layer and may includeAu.

The current spreading layer may have a reflectivity of 65% to 75%.Accordingly, the light emitting diode according to this embodiment canprovide optical reflection by the current spreading layer in addition tooptical reflection by the reflective electrode structure, whereby lighttraveling through the sidewall of the mesa and the first conductive-typesemiconductor layer can be reflected.

The current spreading layer may further include a bonding layer placedon the anti-oxidation layer. The bonding layer may include Ti, Cr, Ni orTa. The bonding layer is used to enhance bonding strength between thecurrent spreading layer and the upper insulation layer, and may beomitted.

For example, the current spreading layer 39 may have a multi-layerstructure including Cr/Al/Ni/Ti/Ni/Ti/Au/Ti.

While the current spreading layer 39 is formed, an anti-diffusionreinforcing layer 40 is formed on the reflective electrode structure 35.The anti-diffusion reinforcing layer 40 and the current spreading layer39 may be formed of or include the same material by the same process.The anti-diffusion reinforcing layer 40 is separated from the currentspreading layer 39. The anti-diffusion reinforcing layer 40 is placedwithin the opening 39 a of the current spreading layer 39.

The anti-diffusion reinforcing layer 40 has a leading end 40 a extendingtherefrom, and the current spreading layer 39 has a leading end 39 bfacing the leading end 40 a. The leading end 40 a may be placed on thelower insulation layer 37 outside the opening 37 a of the lowerinsulation layer 37. However, it should be understood that the disclosedtechnology is not limited thereto. Alternatively, the opening 37 a ofthe lower insulation layer 37 may have a similar shape to the shape ofthe leading end 40 a, and the leading end 40 a may be placed within theopening 40 a of the lower insulation layer 37.

The leading end 39 a of the current spreading layer 39 is placed on thelower insulation layer 37 and is separated from the leading end 40 a.The leading end 39 b and the leading end 40 a define a spark gaptherebetween. As a result, these leading ends 39 b and 40 a may beplaced closer than other portions or may have an angled shape in orderto allow generation of an electric spark between the leading ends 39 band 40 a when high voltage static electricity is applied to a gapbetween the current spreading layer 39 and the anti-diffusionreinforcing layer 40. For example, as shown in FIG. 8, the leading ends39 b and 40 a may have a semi-circular shape or an angled shape and maybe disposed to face each other.

Referring to FIG. 9, an upper insulation layer 41 is formed on thecurrent spreading layer 39. The upper insulation layer 41 has an opening41 a which exposes the current spreading layer 39 to define a firstelectrode pad region 43 a, and an opening 41 b which exposes thereflective electrode structure 35 to define a second electrode padregion 43 a. The opening 41 a may have an elongated shape perpendicularto the branches Mb of the mesa M. The opening 41 b of the upperinsulation layer 41 has a narrower area than the opening 39 a of thecurrent spreading layer 39 and thus the upper insulation layer 41 cancover the sidewall of the opening 39 a.

When the anti-diffusion reinforcing layer 40 is formed on the reflectiveelectrode structure 35, the opening 41 b exposes the anti-diffusionreinforcing layer 40. In this case, the reflective electrode structure35 can be concealed or sealed by the upper insulation layer 41 and theanti-diffusion reinforcing layer 40. Furthermore, the upper insulationlayer 41 has an opening 41 c which exposes at least part of the leadingend 39 b and the leading end 40 a. With this configuration, the sparkgap between the leading end 39 b and the leading end 40 a is exposed,thereby allowing generation of electrostatic discharge by an electricalspark through air.

Further, the upper insulation layer 41 may be formed on the chipisolation region 23 h to cover the side surface of the firstconductive-type semiconductor layer 23. With this configuration, it ispossible to prevent penetration of moisture and the like through upperand lower interfaces of the first conductive-type semiconductor layer.

The upper insulation layer 41 may be formed of or include a siliconnitride layer to prevent diffusion of metal elements from solder pastes,and may have a thickness of 1 m to 2 m. When the thickness of the upperinsulation layer is less than 1 m, it is difficult to prevent diffusionof metal the elements from the solder pastes.

Optionally, an anti-Sn diffusion plating layer (not shown) may beadditionally formed on the first electrode pad region 43 a and thesecond electrode pad region 43 b by electroless plating such as ENIG(electroless nickel immersion gold) and the like.

The first electrode pad region 43 a is electrically connected to thefirst conductive-type semiconductor layer 23 through the currentspreading layer 39, and the second electrode pad region 43 b iselectrically connected to the second conductive-type semiconductor layer27 through the anti-diffusion reinforcing layer 40 and the reflectiveelectrode structure 35.

The first electrode pad region 43 a and the second electrode pad region43 b are used to mount the light emitting diode on a printed circuitboard and the like via solder pastes. Thus, in order to prevent shortcircuit between the first electrode pad region 43 a and the secondelectrode pad region 43 b by the solder pastes, electrode pads may beseparated by a distance of about 300 m or more from each other.

Then, the substrate 21 may be removed to have a small thickness bypartially grinding and/or lapping a lower surface of the substrate 21.Then, the substrate 21 is divided into individual chip units, therebyproviding divided light emitting diode chips. Here, the substrate 21 maybe divided at the chip isolation region 23 h formed by laser scribingand thus there is no need for additional laser scribing for division ofchips.

The substrate 21 may be removed from the light emitting diode chipsbefore or after being divided into individual light emitting diode chipunits.

Referring to FIG. 10, a wavelength conversion layer 45 is formed on thelight emitting diodes separated from each other. The wavelengthconversion layer 45 may be formed by coating a phosphor-containing resinonto the light emitting diodes using a printing technique, or by coatingthe substrate 21 with phosphor powder using an aerosol apparatus. Forexample, aerosol deposition can form a thin phosphor layer with auniform thickness on the light emitting diodes, thereby improving coloruniformity of light emitted from the light emitting diodes. As a result,the light emitting diodes according to the embodiments of the disclosedtechnology are completed and may be bonded to the corresponding pads 53a, 53 b of the printed circuit board 51 by solder pastes, as shown inFIG. 1.

In this embodiment, the first and second electrode pad regions 43 a and43 b exposed by the upper insulation layer 41 are directly mounted onthe printed circuit board. However, it should be understood that thedisclosed technology is not limited thereto. Alternatively, additionalelectrode patterns are formed on the electrode pad regions 43 a and 43 bto form further enlarged pad regions. In this case, however, anadditional photomask for formation of the electrode patterns may beused.

FIG. 11( a) to FIG. 14( c) are views illustrating a method offabricating a light emitting diode in accordance with another embodimentof the disclosed technology, and in each figure, (a) is a plan view, (b)is a cross-sectional view taken along line A-A, and (c) is across-sectional view taken along line B-B.

In the embodiments described above, the mesa M is formed after thereflective electrode structure 35 is formed. In the presentimplementations, the mesa M is formed before the reflective electrodestructure 35 is formed.

First, referring to FIG. 11, as described with reference to FIG. 2, afirst conductive-type semiconductor layer 23, an active layer 25 and asecond conductive-type semiconductor layer 27 are formed on a substrate21. Then, the mesa M is formed by a patterning process. The mesa M issimilar to that described above in FIG. 5, and a detailed descriptionthereof will be omitted.

Referring to FIG. 12, a pre-oxidation layer 29 is formed to cover thefirst conductive-type semiconductor layer 23 and the mesa M. Thepre-oxidation layer 29 may be formed of or include the same material bythe same process as those described with reference to FIG. 2. Aphotoresist pattern 30 having openings 30 a is formed on thepre-oxidation layer 29. The openings 30 a of the photoresist pattern 30are placed in an upper region of the mesa M. The photoresist pattern 30is the same as that described with reference to FIG. 2 except that thephotoresist pattern 30 is formed on the substrate 21 having the mesa Mformed thereon, and a detailed description thereof will be omitted.

Referring to FIG. 13, the pre-oxidation layer 29 is subjected to etchingthrough the photoresist pattern 30 used as an etching mask, so thatopenings 29 a are formed to expose the second conductive-typesemiconductor layer 27 therethrough.

Referring to FIG. 14, as described in detail with reference to FIG. 4,the reflective electrode structure 35 is formed on each mesas M by alift-off technique. Then, light emitting diodes can be fabricatedthrough similar processes to the processes described above withreference to FIG. 6 to FIG. 11.

According to this embodiment, since the mesa M is formed prior to thereflective electrode structure 35, the pre-oxidation layer 29 can remainon side surfaces of the mesas M and in regions between the mesas M.Then, the pre-oxidation layer 29 is covered by the lower insulationlayer 39 and is subjected to patterning together with the lowerinsulation layer 39.

Although various embodiments have been described above, it should beunderstood that other implementations are also possible. In addition,some features of a certain embodiment may also be applied to otherembodiments in the same or similar ways without departing from thespirit and scope of the disclosed technology.

What is claimed is:
 1. A light emitting diode (LED) module comprising: aprinted circuit board; and a light emitting diode bonded to an upperside of the printed circuit board, the light emitting diode comprising:a first conductive-type semiconductor layer; a mesa placed on the firstconductive-type semiconductor layer and including an active layer and asecond conductive-type semiconductor layer; a reflective electrodestructure disposed on the mesa; a current spreading layer covering themesa and the first conductive-type semiconductor layer, and having anopening exposing the reflective electrode structure, the currentspreading layer being electrically connected to the firstconductive-type semiconductor layer while being insulated from thereflective electrode structure and the mesa; and an upper insulationlayer covering the current spreading layer, the upper insulation layerhaving a first opening exposing the current spreading layer to definethe first electrode pad region, and a second opening exposing an exposedupper region of the reflective electrode structure to define the secondelectrode pad region, wherein the first electrode pad region and thesecond electrode pad region are bonded to corresponding pads on theprinted circuit boards via solder pastes, respectively.
 2. The LEDmodule of claim 1, wherein the light emitting diode further comprises ananti-Sn diffusion plating layer formed on the first electrode pad regionand the second electrode pad region.
 3. The LED module of claim 1,wherein the light emitting diode further comprises an anti-diffusionreinforcing layer disposed on the reflective electrode structure in theopening of the current spreading layer, the anti-diffusion reinforcinglayer being exposed through the second opening of the upper insulationlayer.
 4. The LED module of claim 3, wherein the anti-diffusionreinforcing layer is formed of the same material as that of the currentspreading layer.
 5. The LED module of claim 4, wherein the currentspreading layer comprises an ohmic contact layer, a reflective metallayer, an anti-diffusion layer, and an anti-oxidation layer.
 6. The LEDmodule of claim 5, wherein the anti-diffusion layer comprises at leastone metal layer selected from the group consisting of Cr, Ti, Ni, Mo,TiW and W layers, and the anti-oxidation layer comprises an Au, Ag ororganic material layer.
 7. The LED module of claim 6, wherein theanti-diffusion layer comprises at least two pairs of Ti/Ni or Ti/Crlayers.
 8. The LED module of claim 5, wherein the current spreadinglayer further comprises a bonding layer disposed on the anti-oxidationlayer.
 9. The LED module of claim 4, wherein the solder paste adjoinsthe current spreading layer and the anti-diffusion reinforcing layer.10. The LED module of claim 1, wherein the reflective electrodestructure comprises: a reflective metal section; a capping metalsection; and an anti-oxidation metal section, the reflective metalsection having a slanted side surface such that an upper surface of thereflective metal section has a narrower area than a lower surfacethereof, and wherein a stress relief layer is formed at an interfacebetween the reflective metal section and the capping metal section. 11.The LED module of claim 1, wherein the mesa comprises elongated branchesextending parallel to each other in one direction and a connectingportion at which the branches are connected to each other, and theopening of the current spreading layer is disposed on the connectingportion.
 12. The LED module of claim 1, wherein the light emitting diodefurther comprises a lower insulation layer disposed between the mesa andthe current spreading layer and insulating the current spreading layerfrom the mesa, the lower insulation layer having an opening that isdisposed in an upper region of the mesa and exposes the reflectiveelectrode structure.
 13. The LED module of claim 12, wherein the openingof the current spreading layer has a greater width than the opening ofthe lower insulation layer such that the opening of the lower insulationlayer is completely exposed therethrough.
 14. The LED module of claim13, wherein the light emitting diode further comprises an anti-diffusionreinforcing layer disposed within the opening of the current spreadinglayer and the opening of the lower insulation layer, the anti-diffusionreinforcing layer being exposed through the second opening of the upperinsulation layer.
 15. The LED module of claim 14, wherein the lowerinsulation layer comprises a silicon oxide layer and the upperinsulation layer comprises a silicon nitride layer.
 16. The LED moduleof claim 1, wherein the solder paste comprises Sn—Ag alloys, Sn—Bialloys, Sn—Zn alloys, or Sn—Ag—Cu alloys.
 17. A light emitting diodecomprising: a first conductive-type semiconductor layer; a mesa disposedon the first conductive-type semiconductor layer and comprising anactive layer and a second conductive-type semiconductor layer; areflective electrode structure disposed on the mesa; a current spreadinglayer covering the mesa and the first conductive-type semiconductorlayer, and having an opening exposing the reflective electrodestructure, the current spreading layer being electrically connected tothe first conductive-type semiconductor layer while being insulated fromthe reflective electrode structure and the mesa; and an upper insulationlayer covering the current spreading layer, the upper insulation layerhaving a first opening exposing the current spreading layer to define afirst electrode pad region, and a second opening exposing an exposedupper region of the reflective electrode structure to define the secondelectrode pad region.
 18. The light emitting diode of claim 17, furthercomprising: an anti-diffusion reinforcing layer disposed on thereflective electrode structure in the opening of the current spreadinglayer, wherein the anti-diffusion reinforcing layer is exposed throughthe second opening of the upper insulation layer, and is formed of thesame material as that of the current spreading layer.
 19. The lightemitting diode of claim 18, further comprising: anti-solder diffusionlayers formed in the first opening and the second opening.
 20. The lightemitting diode of claim 18, wherein the current spreading layercomprises an ohmic contact layer, a reflective metal layer, ananti-diffusion layer, and an anti-oxidation layer.
 21. A method offabricating a light emitting diode, comprising: forming a firstconductive-type semiconductor layer, an active layer and a secondconductive-type semiconductor layer on a substrate; patterning thesecond conductive-type semiconductor layer and the active layer to forma mesa on the first conductive-type semiconductor layer while forming areflective electrode structure on the mesa to form ohmic contact withthe mesa; forming a current spreading layer covering the mesa and thefirst conductive-type semiconductor layer, and having an opening thatexposes the reflective electrode structure, the current spreading layerforming ohmic contact with the first conductive-type semiconductor layerwhile being insulated from the mesa; and forming an upper insulationlayer covering the current spreading layer, the upper insulation layerhaving a first opening exposing the current spreading layer to define afirst electrode pad region, and a second opening exposing an exposedupper region of the reflective electrode structure to define the secondelectrode pad region.
 22. The method of claim 21, further comprising:forming an anti-diffusion reinforcing layer on the reflective electrodestructure, wherein the anti-diffusion reinforcing layer is formedtogether with the current spreading layer, and the second opening of theupper insulation layer exposes the anti-diffusion reinforcing layer. 23.The method of claim 22, further comprising: forming a lower insulationlayer covering the mesa and the first conductive-type semiconductorlayer, before forming the current spreading layer; dividing the lowerinsulation layer and the first conductive-type semiconductor layer intochip regions by laser scribing; and patterning the lower insulationlayer to form openings exposing the first conductive-type semiconductorlayer and an opening exposing the reflective electrode structure. 24.The method of claim 23, wherein the lower insulation layer comprises asilicon oxide layer and the upper insulation layer comprises a siliconnitride layer.
 25. The method of claim 24, further comprising: ananti-Sn diffusion plating layer formed on the first electrode pad regionand the second electrode pad region using a plating technique.